ANSWER
Any value of r in between -1 and 0 (exclusive on both sides).
For example, r = -0.1 or r = -0.5
EXPLANATION
You did not specify any answer choices; all we can do is state a range of values for r.
We have exponential function \(A(x) = P(1 + r)^x\)
We note that the base is "1 + r"
For an exponential function to be a decay function, the base must be between 0 and 1 exclusive.
\(\begin{array}{r c c c l l}
0 &\ \textless \ & 1 + r &\ \textless \ & 1 \\
-1 &\ \textless \ & r &\ \textless \ & 0 & (\text{\footnotesize Solve for $r$ by subtracting 1 from everything})
\end{array}\)
Therefore, the values for r must lie in the range -1 < r < 0 (between -1 and 0 exclusive)
In interval notation, this is expressed as (-1, 0)
